This invention relates to capacitive membrane ultrasound transducers (cMUTs). In particular, the invention relates to bias voltages used with electrostatic transducers.
Electrostatic transducers, such as micro-machined capacitance based electrostatic transducers, offer many advantages over traditional ceramic transducers. For example, electrostatic transducers may be cheaper to manufacture, allow higher manufacturing yields, provide more size and shape options, use non-toxic materials, and have higher bandwidth. However, electrostatic transducers require a bias voltage for operation. The bias voltage in combination with any transmit voltage is limited to avoid collapse of the membrane. The electrostatic attraction of the membrane cannot exceed the membrane tension. Likewise, the dielectric breakdown of the gap between electrodes cannot be exceeded. The bias voltage should also be larger than the peak voltage of the transmit voltage to avoid harmonic distortion.
The magnitude of the transmit voltage waveform sets a requirement on the bias voltage. Accordingly, the bias voltage is set for operation during transmit and is not optimum for operation during reception of acoustic signals.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a method and system for operating a capacitive membrane ultrasound transducer. The bias voltage applied to one or more elements of the transducer is controlled for optimum performance.
In a first aspect, a bias voltage is applied to the transducer in a receive mode. The bias voltage is varied as a function of time, such as to provide for depth gain compensation.
In a second aspect, a bias voltage is applied to the transducer. Different bias voltages are applied to elevationally spaced sub-elements of one of the multiple elements of the transducer.
In a third aspect, a bias voltage is applied to the transducer. The bias voltage is varied as a function of the imaging mode of operation.
In a fourth aspect, a bias voltage is applied to the transducer. A radio frequency signal is applied with the bias voltage.
In a fifth aspect, a first bias voltage is applied to an element in a receive mode. A second different bias voltage is applied to the element in a transmit mode. A transmit waveform is applied to the element. The bias is changed from the first to the second bias voltage substantially simultaneously with a beginning of the transmit waveform.
In a sixth aspect, a first bias voltage is applied to a first sub-element of one of the elements of the transducer. A second, reversed polarity bias voltage is applied to a second sub-element of the element.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.